1. Field of the Invention
This invention relates to a process and an aritcle prepared according to this process. More specifically, this invention involves a process for preparation of transparencies.
2. Description of the Prior Art
The methods for recording of image information on photosensitive materials are many and varied. Generally, in such systems, image information is projected onto a photosensitive medium and the medium either visually or invisibly (chemically or electrically) altered. In order to develop such invisible alteration of the photosensitive medium, the altered and/or unaltered areas of the photosensitive medium are brought in contact with an additional material or agency which facilitates the manifestation of such differences either in the form of a change in color and/or a change in optical density or both. In classical silver halide photography, image formation results from the irreversible chemical reduction of a silver salt in the exposed areas of the photographic emulsion and the selective removal of the unreduced silver from the emulsion. Depending upon the particular photographic emulsion and developing process, the image can be recorded either positively or negatively on the photosensitive medium.
More recently, there has been disclosed a migration imaging system wherein photosensitive or non-photosensitive particles are selectively caused to migrate from (or just below) the surface of a softenable material into the bulk of said material in response to image information, U.S. Pat. Nos. 3,556,781 and 3,653,885. In a typical embodiment of such a migration imaging system, a migration imaging member which consists essentially of a layer of softenable or soluble material containing migration material coated on a conductive substrate is prepared and an electrostatic latent image is formed on the surface of this softenable layer. The softenable layer is then developed by heating or by contacting said layer with a solent or vapors of a solvent which attacks only the softenable layer. A portion of the migration material will migrate through this softenable layer during development and in certain instances deposit in imagewise configuration on the conductive substrate. Those particles which do not migrate to the conductive substrate can be removed along with the softenable layer through the use of solvents. The imaging members used in such migration imaging processes can have three distinct structures: a layered configuration, which comprises a conductive substrate, a layer of softenable material and an overcoating of migration material (usually particulate) embedded in the upper surface of the softenable layer; a binder structure in which the migration material is dispersed throughout the softenable layer; and, thirdly, an overcoated structure in which the conductive substrate is overcoated with a layer of softenable material followed by a layer of migration material and a second overcoating of softenable material, thus sandwiching the migration material therebetween. Where the non-imaged portion of the migration materials are not removed, the resultant image appears against a background of such materials. It has been suggested that such background may be reduced by simply heating of the image member, U.S. Pat. No. 3,556,781 -- column 3, lines 49-53.
In still yet another imaging system, a precursor (an "organo-metallo" compound) is initially dispersed in an amorphous glass matrix and chalcogens selectively extruded therefrom in response to (a) exposure of said layer to imagining energy followed by a second exposure to development energy; (b) simultaneous exposure of the dispersion to both imaging and development energy; or (c) simply exposure of the dispersion to imaging energy; German Patent Application OLS No. 2,233,868 (priority being claimed to U.S. patent application Ser. No. 163,891 now abandoned filed July 19, 1971). The glassy matrix within which such chalcogen deposition cakes place, must be capable of trapping intermediate compounds, radicals and charge carriers generated during exposure to imaging energy in order to enable subsequent thermal development and/or enhancement of the desired chalcogen deposit. Chalcogen formation is manifest within this glassy matrix by the appearance of a permanent, dense, highly visible deposit conforming to the image input. Unfortunately, the above system is not readily capable of fixation, that is, inadvertent exposure of the imaged film to additional stimuli can result in the unwanted deposition of additional chalogen materials and thuscan seriously impair or destroy the previously formed image pattern.
As is evident from the above discussion, it is generally necessary to either remove or modify the background portions of the imaged member in order to enhance image contrast. In a typical silver halide photographic system, this is achieved by chemical means. In the migration imaging systems, image background is reduced by removal of the non-migrated materials or by thermal modification thereof, subsequent to development. In each instance, the imaged member is irrevisibly modified and cannot be further imaged by exposure to additional image information. Although the imaging system described in the above referenced German publication does possess the capability of having further image information added onto the previously imaged dispersion, such a capability is in fact a serious limitation on both the use and storage of the product of this imaging system.
It is thus apparent that although it would be desirable to have an imaging member capable of producing high resolution images in response to image information without the necessity of separate development and fixation of the image pattern, the systems presently available for achieving such results are seriously deficient with regard to their ability to be rendered further insensitive to image input in order to avoid inadvertent and undesirable alteration of the previously formed image pattern.
Accordingly, it is the object of this invention to remove the above as well as related deficiencies in the prior art.
More specifically, it is the principal object of this invention to provide a process for preparation of transparencies which can be modified by the exposure thereof to additional image information.
it is an additional object of this invention to provide an imaging process for preparation of transparencies which does not require the use of liquid chemicals or solvent vapors in either the development or the fixation of the image pattern within the transparency.
It is yet an additional object of this invention to provide a process for the preparation of transparencies which can prevent the inadvertent recording of image information on the transparency and yet retain the ability of the transparency for recording additional image information.
Further objects of this invention include the preparation of transparencies by the above process.